Hodgkin, Huxley, and Katz did experiments that helped explain... One day, they measured the normal cytoplasm for an ion we will call "X". They then made an artificial cytoplasm that had a lot more "X" in it than normal. They replaced the normal cytoplasm of a squid axon with their artificial cytoplasm and then sealed the cut end of the axon. The resting membrane potential was then measured and found to be -100mV instead of the normal -80 mV. What must ion "X" be?

K+

Which of the following changes have the potential to dramatically affect the potential difference across the plasma membrane?

Increased permeability of the membrane to sodium ions and increased intracellular concentration of potassium ions.

Opening of sodium gates typically leads to ________.

depolarization of the plasma membrane

Which of the following will cause the plasma membrane to hyperpolarize when at its RMP?

inflow of chloride

Mr. Miller has been hospitalized for the flu. The flu virus increases membrane permeability to potassium. You would expect his cells to _________.

hyperpolarize

For the resting membrane potential, increasing the sodium ion concentration in the ECF results in ________.

little change in membrane potential

Which of the following statements accurately describe events that occur as a result of a local potential reaching threshold?

Inactivation gates of Na+ ion channels begin to open and a positive feedback cycle develops in which depolarization causes activation gates of Na+ ion channels to open.

Which of the following events will lead to depolarization?

An increase in K+ ions in the extracellular fluid.

In hyperpolarization _________.

K+ ions tend to diffuse out of the cell

If the charge difference across the plasma membrane is decreased, _________.

the membrane potential is more positive

Voltage-gated sodium channels are sensitive to changes in the extracellular concentration of _________.

calcium ions

Which of the following situations will lead to hyperpolarization?

None of these situations will lead to hyperpolarization.

Depolarization of the nerve cell membrane occurs when there is a rapid influx (inflow) of _________.

Sodium Ions

Burn patients experience the destruction of cells and the release of cellular contents into the ECF. Burn patients are more likely to suffer from which of the following conditions?

tachycardia (a rapid heart rate)

If the ECF around a nerve cell is replaced with an isotonic saline solution that contains potassium ions and other solutes at concentrations very close to the ECF concentrations of a normal cell, the result is ________.

a resting membrane potential close to its normal value

A local anesthetic such as Novocaine decreases membrane permeability to Na+ ions. The use of this anesthetic will __________.

block sensory input into the CNS

Predict the effect on the resting membrane potential if concentration of potassium ions in the extracellular fluid increases.

The increased extracellular potassium concentration decreases the normal potassium ion gradient. As a result, there is less of a tendency for potassium ions to diffuse out of the cell and the RMP is less negative; that is, it depolarizes

Predict the effect on the resting membrane potential if there is an increase in the permeability of the plasma membrane to potassium ions.

With an increase in membrane permeability to potassium ions, a larger number of potassium ions diffuse out of the cell. This makes the inside of the cell more negative when compared to the outside of the cell and results in hyperpolarization.

Predict the effect on the resting membrane potential if permeability of cell membrane to sodium ions increases.

When the permeability to sodium ions increases, the sodium ions diffuse into the cell and the inside of the cell becomes more positive, resulting in depolarization.

Predict the effect on the resting membrane potential (RMP) if extracellular concentration of sodium increases (a small to medium amount).

The resting membrane is not very permeable to Na+, so there very little change in RMP.

If the permeability of the plasma membrane to K+ increases, the resting membrane potential difference _______. This is called _______.

increases, hyperpolarization

Decreasing the extracellular concentration of K+ affects the resting membrane potential by causing

hyperpolarization.

Which of these terms is correctly matched with its definition or description?

hyperpolarization: membrane potential becomes more negative

Which of the following statements about action potentials are correct?

-ALL THE ABOVE ARE CORRECT-

There is a decrease in Na+ permeability and an increase in K+ permeability during the repolarization phase of the action potential.

The threshold can be reached in response to a decrease in K+ permeability.

The rising phase of the action potential is due to a rapid increase in the permeability to Na+.

The hyperpolarizing after potential is due to which of the following?1. hyperkalemia2. increased permeability to Cl-3. hypercalcemia4. hyponatremia5. inability of Na+ channels to open

2

A Na+ channel opens in response to the finding of a ligand. Which of the following may occur as a result?(1) A change in the membrane potential to equal a value closer to zero.(2) A change in the membrane potential to equal a value that is more negative.(3) A sudden movement of Na+ out of the cell.(4)A sudden inactivation of Na+ moving into the cell.

1

Which of the following is MOST likely to lead to a resting membrane potential changing to a value that reaches threshold?

Decreased extracellular Ca++

During the depolarization phase of an action potential, the permeability of the plasma membrane to:

Na+ increases

Depolarization of the cell membrane occurs when there is a rapid influx (inflow) of _______

sodium ions.

An action potential ________.

occurs when the local potential reaches threshold level

Blocking ____________ channels would prevent neuronal depolarization.

Na+

During an action potential _______.

Na+ influx causes depolarization

The minimum depolarization needed to open Na+ gates is called the ________.

threshold

When a neuron is excited:

-All of the Above is correct-

-the nerve cell membrane becomes permeable to sodium

-an impulse begins to flow

-the nerve fiber becomes depolarized

-positive charges move in

Local potentials are ___, whereas action potential are ___.

graded; all or none

Which of the following events is NOT a characteristic of an action potential?

As sodium ions enter, the inside of the plasma membrane becomes more negative.

A stimulus either causes an action potential or it doesn't. This is called ________.

an all-or-none response

The opening of more and more Na+ ion channels during depolarization __________.

is an example of a positive feedback cycle

During depolarization of the plasma membrane, _________.

sodium ions move rapidly into the cell

Each voltage-gated Na+ ion channel has two voltage sensitive gates: an activation gate and an inactivation gate. Which of the following would occur during depolarization?

Both activation and inactivation gates are open.

The figure illustrates the Action Potential. What does "A" represent?

local potential

The figure illustrates the Action Potential. What does "B" represent?

depolarization

The figure illustrates the Action Potential. What does "C" represent?

repolarization

The figure illustrates the Action Potential. What does "D" represent?

threshold

The figure illustrates the Action Potential. What does "E" represent?

afterpotential

Graded potentials

All of these are correct.

Can summate.spread over the plasma membrane in decremental fashion.

Are confined to a small region of the plasma membrane.

Are not propagated for long distances.

During the depolarization phase of an action potential, the permeability of the membrane

to Na+ is greatly increased.

During repolarization of the plasma membrane,

K+ diffuse out of the cell.

A subthreshold stimulus

produced a graded potential.

Consider the following Case

A 30-year-old woman is brought into the emergency room. The patient had been dining in a local restaurant, and while eating dessert she noted the following symptoms: Initially there was tingling sensation that affected the mouth and lips, but then it spread to the face and neck. Then the tingling spread down the arms and legs

-Both A and B are supported-

This finding suggests that there could be a defect in the function of the Na+ channels.

If a smaller number of Na+ channels than normal were participating in the action potential, a slower rate of rise and a smaller amplitude of the action potential would be expected.

A second action potential cannot be generated until _________________________.

the majority of the sodium activation gates are closed

When repolarization of the cell membrane is complete, the _________.

original polarity of the cell is restored

The very brief moment following stimulation when a muscle remains unresponsive to additional stimulation is called the ________.

refractory period

The period of time when Na+ channels are recovering from their inactive state and K+ channels are still open is the _________.

Both repolarization and relative refractory period are correct.

In order for sodium to be pumped out of a neuron, _________ must occur.

an expenditure of energy

A neuron repolarizes by ________ after it has been stimulated.

the outward movement of potassium ions (K+)

During hyperpolarization (or afterpotential) _______.

potassium ions are leaving the cell

When the voltage of a plasma membrane shifts from +35mV towards 0 mV, we say the cell is _______.

repolarizing

During the absolute refractory period _______.

no stimulus of any strength will trigger a new action potential

In some cells, an afterpotential occurs because _________.

there is prolonged, elevated permeability to potassium during repolarization

When repolarization of a neuron is complete, the __________.

original polarity of the neuron is restored

During the absolute refractory period, the cell _________.

is insensitive to further stimulation

The absolute refractory period assures ___________.

completion of repolarization before another action potential

The absolute refractory period ends when _________.

inactivation gates of voltage-gated Na+ ion channels reopen.

In nerve physiology, the time soon after an action potential has moved on and the sodium gates are unable to open is called the __________.

refractory period

While the membrane is depolarizing its __________.

sodium gates are fully open

The absolute refractory period

-Both A and B are correct

-Is the period of time when a strong stimulus can initiate a second action potential.

-Limits how many action potentials can be produced during a given period of time.

Conduction of an action potential in a myelinated axon is called _________.